Stress

Definition



The concept of homeostasis refers to relatively stable and optimal conditions for cellular, organ and systemic functioning of the body. A stressor is a factor that challenges physiological functioning, health, wellbeing, survival or reproduction; by creating instability and producing a stress response. Thus; a stressor is a stimulus that elicits a physiological response directed to re-attain homeostasis, balance or viable conditions within the organism after it has been altered. Stress responses enable the organism to maintain physiological systems within functional limits as changes in conditions occur.
In this sense; “stress” is a state of unbalanced or altered organic conditions caused by a stressor. Long term exposure to a stressor may lead to physiological adaptations in individuals. An adaptation is the re-attainment of regular functioning, or the achievement of improved performance in the new conditions created by a stressor. However; failure to respond and adapt to a stressor will compromise physiological functioning and survival, if the exposure to the stressor is sufficiently chronic and provokes severe disturbance.



Biology of The Stress Response



A stress response results from exposure or perceived exposure to a stressor (danger or threat). “The stress response is better understood as a way in which individuals regulate their physiology in response to daily activities and environmental conditions…” [1] . A network between the nervous and endocrine systems, signals other organs in the body to adapt their functioning to cope with the stressor. These mechanisms function by activating and suppressing physiological processes to facilitate a “fight or flight response”. In non-human animals this response is induced by threats to survival and reproduction. In this case; generally short-term responses occur in sporadic episodes.


Stress in Humans

In humans the stress response is generally characterized by a chronic perception of a threat or stressor. The evolution of the human nervous system conferred consciousness, extensive memory, and the ability to imagine what might happen in the future. This enables humans to experience psychological stress by provoking anticipatory behavioral and physiological responses [2] [3] . Imagination can trigger a physiological stress response, even in absence of a true threat. Social stressors like violence, food scarcity, unemployment, financial problems, social stratification, and others; can also be perceived as threats and elicit the response. While the perception of what is stressful, and physiological manifestations of stress vary cross-culturally and individually; social circumstances are the most common stressors in humans.

Physiological Processes Elicited During “Fight or Flight Response”

Since the “fight of flight response” is activated to adapt the physiological functioning of an organism to a new challenge that has arisen; it prepares essential parts of the body for sudden and vigorous physical exertion. The response increases energy availability, inhibit maintenance activities and long-term growth. Metabolic functioning directs energy production and expenditure for short-term immediate survival. The feeling of pain is decreased and the memory is sharpened. The sympathetic nervous system is activated and controls the stress response. While this is happening, the activity of the parasympathetic nervous system, which controls digestion, reproduction and growth, is suppressed. This provides more nutrients for energy production and use more available to tissues like muscle. The body becomes better prepared for responding rapidly to a threat; hence incrementing the likelihood of momentary survival. As essential for survival as this is; a chronic activation of the stress response compromises other physiological functions on the long-term, assisting susceptibility to disease.

Hormonal Stress Response

A secondary and slower response to threats is mediated by the endocrine system. These hormonal responses can stay activated for extended periods of time. The primary hormonal pathway is controlled by the hypothalamic-pituitary-adrenocortical axis (HPA). A perceived threat triggers the secretion of corticotrophin-releasing hormone (ACTH) by the hypothalamus, which stimulates the pituitary gland to produce corticotrophin (ACTH). ACTH is then released into the bloodstream, and signals the adrenal glands to produce the hormone cortisol. A section of the brain, called the hippocampus is also responsible in the regulation of cortisol levels.

Cortisol

Various organs and tissues in the body are sensitive to cortisol and are equipped with cortisol receptors (kidneys, immune system, liver, muscle, reproductive organs). This hormone regulates organ functioning by binding to the tissues and suppressing or stimulating their activity. Cortisol plays an important role in replenishing glucose and fat energy stores in tissues by enabling fat deposition and glycogen synthesis. In short-term stress responses, it enables the immune system to work more efficiently at attending injuries that may be caused by the imminent threat. However; long-term activation of this mechanism provides extended exposure to high cortisol levels, and affects the organism by suppressing immune function.

Allostasis

Allostasis refers to regulatory systems in which there are no clear set points, where there are individual differences in expression [4] , the behavioral and physiological responses are anticipatory[5] [6] , and there is vulnerability to physiological overload and the breakdown of regulatory capacities [7] . The concept of homeostasis presents a static regulatory system, while in allostasis the normal range shifts

in response to environmental stressors.

Allostatic Load

During allostatic regulation, chronic and high level of exposure to stressors may occur. When this happens, the stress responses are maintained activated constantly; and the costs for maintaining the stress responses activated, compromises regular physiological functioning and health. This is known as allostatic load or allostatic over-load.

Negative Consequences of Chronic Stress

The cardiovascular system is directly affected by the continuous and prolonged activation of this mechanism. The “fight or flight response” that increased the blood pressure, now contributes to the development of hypertension, atherosclerosis, myocardial infarction, and stroke. The immune system is affected negatively because the long-term exposure to an activated stress response produces immune suppression and autoimmune responses. Growth (stunting) and development is affected. Metabolic disturbances like the increase of glucose and fat levels in blood, and reduction or augmentation of insulin; can lead to insulin resistance/diabetes and metabolic syndrome. Neurological functions as memory, also become adversely affected.

Stress, Growth and Development

Stress during pregnancy cues the fetus of a stressful extra-uterine environment [8] . Low birth weight is inversely associated with high levels of cortisol [9] . Decreased cortisol receptors in brain areas that control the stress response, further complicates the situation, and impaired growth results [10] . Accelerated development in sexual maturation, early menarche, and first birth at earlier age are also reported as effects of high levels of stress on development [11] [12] [13] . Higher cortisol levels also effects immune function in children, as it is associated with more frequent infections [14] . Social protective factors like nurturing and feeling security decrease cortisol levels; while parental absence, abuse and neglect raises cortisol levels [15] [16] .

Evolutionary Perspectives

Wiley and Allen (2009)[17] argue that humans in the past lived in egalitarian small groups, and that contemporary sources of stress, like social and economic inequality are relatively new for our species. According to this idea; it seems that we might not be well adapted to a chronic activation of the stress response, and for this reason it is detrimental for our health. However; Daniel Lende points out that our primate ancestors have been exposed to within-species social hierarchies, for approximately 25 million years [18] . For this reason, it would be expected that humans and other extant socially complex primates should be well adapted to psychosocial stress. In this sense; other particular aspects of social inequality might provide more comprehensive explanations.



Social Aspects of Stress (Psychosocial Stress)



Social conditions can also contribute to psychological and physiological stress. Stress responses induced by social and psychological factors are known as psychosocial stressors. In this case; social conditions or social stresses cause psychological stress, which in turn provokes a physiological stress response. Daniel Lende argues that feelings of unpredictability, lack of control, and higher stakes are at risk; are the three main reasons for experiencing psychosocial stress [19] .


Contribution of Social Inequality to Stress Related Diseases (The Embodiment of Inequality)

In studies examining the relationship between social inequality, stress and disease; it has been found that the greater the wealth, the better the health [20] [21] [22] [23] . On average; countries that have wealth more evenly distributed, have better health than countries with more marked socioeconomic disparities. Life expectancy is also influenced by these; as more income inequality means lower average life expectancies. In contrast; less differences in socio-economic gradient means higher life expectancies. Even within wealthy countries, status differentials are good predictors of health outcomes. The Whitehall studies analyzed the relationship between social inequality and health. These studies examined the British civil service, which is composed of a very clear, highly stratified class ranking of employees. A clear relationship between social hierarchy and health was found. This relationship showed that the socio-economic hierarchical gradient follows the same pattern of disease in this population[24] [25] [26] .

The higher the class, the better the health. The lower the class, the worse the health. This is particularly significant, as Britain has a universal healthcare system that provides equal access for every individual. In this case, the variable of differential access to healthcare has been controlled by the nature of this system. Risky health behaviors like unhealthy dietary practices, lack of physical activity, and smoking are more frequent in the lower strata, have been taken into consideration. However; these differences were only able to explain less than one third of the difference in health outcomes within the hierarchy [27] . There is a persistent idea that genetic or “racial” differences could explain health disparities. Yet, all socio-economic groups within the developed countries have experienced significant health improvements due to public health efforts during the decades. There is no evidence supporting a genetic basis for this health differential. Wiley and Allen (2009)[28] argue that if the poor were genetically inferior, they would not have been able to show this kind of improvement. Relative wealth and status, social cohesion and social participation, and sources for social support, are relevant social factors that are directly related to suffering of chronic stress and adverse health outcomes [29] [30] [31] .

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In Scandinavian countries where there is a more even distribution of resources across the society, the health gradient is not as evident as in wealthy countries that have more social inequality. It has been found that the redistribution of resources improves the health status of individuals in all social classes, but in particular the ones in the lowest rankings [32] . In addition to this; the higher the unemployment rates are in a society, the worse the health status of the population[33] . On the other hand; highly hierarchical societies provide fewer opportunities for social participation and network formation for the lower classes, because they are less integrated [34] [35] . It has also been reported that individuals that experience the feeling of having an inconsistency between what is desired and what can actually be attained, have a higher probability of developing high blood pressure [36] [37] . In the case of adolescents that live in households with higher levels of lifestyle incongruence between what is desired or needed and what is available; suffer from significant immunosuppression [38] .

How “Race” and Ethnicity Affect Health? (The Embodiment of “Race” and Inequality)

The concept of “race” as a measurable and distinguishable, biological or genetic categorization; is outdated and scientifically discredited. Biological variation is continuous within and across populations. There are no exclusive traits that sharply differentiate populations; instead, traits are found in different frequencies among different populations [39] . For this reason, the criteria for “racial classification” vary greatly from place to place and from time to time. “Race” can be best understood as a socio-cultural construct based on cultural interpretations and perspectives. However; some authors still argue that even if the concept of “race” does not have any biological value, it is still valuable for performing categorizations based on social or ethnic characteristics [40] .

Currently; the United States is the only of the wealthy countries that does not report social class in the vital statistics records [41] . However; “race” is commonly used in the census and as a research variable in the United States [42] . The general assumption behind this is that “races” represent genetic characteristics that affect the health of individuals of African descent differently from the individuals of European descent [43] [44] . In reality; all peoples that are considered “non-white” in the United States are minorities that reflect a low socio-economic status [45] . It is now well known that socio-economic status and geographical residence explains better the health disparities between the so called “races” in the United States [46] . Assumptions about “race” determined health disparities fail to acknowledge that social conditions like poverty, violence, and instability, alters biological development [47] [48] (See the second video about epigenetics and gene expression). Racism and discrimination are very influential factors that contribute to these social and health inequalities.

Psychosocial stress is caused by perceived racial discrimination [49] [50] . Within African Americans; individuals with the darker skin pigmentation receive greater levels of discrimination than the individuals with lighter skin pigmentation [51] . In addition; dark skinned patients are less likely to be referred for treatment than light skinned patients even when both are reporting identical cardiac symptoms [52] . The high prevalence of hypertension and other other health disparities in African Americans might be to a great degree attributed to the stress response provoked by racism, social inequality and economic deprivation [53] .



Discussion Board







External Media Links




Stress Response: Savior to Killer. Robert Sapolsky.
http://www.youtube.com/watch?v=sPS7GnromGo

When the Bough Breaks: Kim Anderson's Story. Unnatural Causes.
http://www.youtube.com/watch?v=sdFzwPEfRhs

Bad Sugar: Water Rights and Diabetes in Arizona. Unnatural Causes.
http://www.youtube.com/watch?v=3pXzbTHhZGQ

Becoming American: Wealth Equals Health. Unnatural Causes.
http://www.youtube.com/watch?v=NqzsMW8B0u4

In Sickness and In Wealth: Health in America. Unnatural Causes.
http://www.youtube.com/watch?v=w98GSXBEyQw

The Mystery of Black-White Differences in Infant Mortality. Unnatural Causes.
http://www.youtube.com/watch?v=INc1a6u8yP4

The Story of Race: A History. American Anthropological Association.
http://www.youtube.com/user/UnderstandingRace#p/a/u/0/No5ai6LZLFg

RACE: Are We So Different? American Anthropological Association.
http://www.youtube.com/user/UnderstandingRace#p/a/u/1/8aaTAUAEyho

Living in Disadvantaged Neighborhoods is Bad for Your Health
http://www.youtube.com/user/unnaturalcausesdoc#p/u/11/pzafgHG7EFE

The Epigenetics of Identical Twins
http://www.youtube.com/watch?v=AV8FM_d1Leo

Epigenetics Neil Degrasse Tyson
http://www.youtube.com/watch?v=LcaRTDsLmiA

What Does Hypertension Do?
http://www.youtube.com/watch?v=fUcLrdPJurU

How Racism Impacts Pregnancy Outcomes
http://www.youtube.com/watch?v=k8fuzh4d544


References




Dressler, W.W. 1992 Culture, Stress, and Depressive Symptoms: Building and Testing a Model in a Specific Setting. In Anthropological Research: Process and Application J. J. Poggie, B. R. DeWalt, and W. W. Dressler, eds. Pp. 19-34. Albany: State University of New York Press.


Dressler, W.W. 1995 Modeling Biocultural Interactions: Examples from Studies of Stress and Cardiovascular Disease. Yearbook of Physical Anthropology 38:27-56.


Leaderman S.A, V. Rauh, L. Weiss, J.L. Stein, L.A. Hoepner, M. Becker, F.P. Perrera. 2004 The Effect of the World Trade Center Event on Birth Outcomes Among Term Deliveries at Three Lower Manhattan Hospitals. Environmental Health Perspectives. 112 (17):1772-1778.


Marmot, Michael. 2004 The Status Syndrome: How Social Standing Affects our Health and Longevity. New York: Henry Holt.


McEwen B.S. 1998 Protective and damaging effects of stress mediators. New Engl. J. Med. 338: 171-179.


McEwen B.S, Stellar E. 1993 Stress and the individual: Mechanisms leading to disease. Arch. Intern. Med. 153: 2093-3101.


Sapolsky R.M. 2004 Why Zebras Don't Get Ulcers? Holt Paperbacks, 3rd Edition. Pp 126-158.


Schulkin J. 2003 Rethinking Homeostasis: Allostatic Regulation in Physiology and Pathophysiology. A Bradford Book, The MIT Press, Cambridge, Massachusetts, London, England.


Wiley S.A, Allen J.S. 2009 Medical Anthropology: A Biocultural Approach. New York, Oxford. Oxford University Press.


Wilkinson, Richard G. 1996 Unhealthy Societies: The Afflictions of Inequality. New York: Routledge.




Works Cited


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